The invention relates generally to a fiber optic sensor for the detection of the movement or position of a component with a ferromagnetic portion. The fiber optic sensor includes a light transmitter, a light guide, and an optical modulator with a permanent magnet and modulator part, all mounted in a housing. Both the light guide and light transmitter are connectable to an electronic analyzing system. The optical modulator part is mounted to be movable relative to the light transmitter and light guide.
A fiber optic sensor of the relevant type for the detection of the speed of rotation of a shaft is described in the Unexamined Published German Patent Application (German Offenlegungsschrift) No. 2,730,737 and in German Patent Specification No. 3,401,858, wherein the shaft is provided with a movement generator constructed for example as a toothed wheel or as a hexagonal nut. The sensor exhibits, in a housing, a transmitting light guide constructed as a light transmitter and a receiving light guide, which are connected to an electronic analysis system connected downstream. In this arrangement, the light irradiated by a light source via the transmitting light guide is coupled into the receiving light guide via an optical modulator, which at the same time represents the movement generator in a form in which the quantity of light is varied, the modulation frequency being utilized as a measure of the speed of rotation of the shaft and appropriately analyzed. The essential advantages of such fiber optic sensors are:
rapid, reaction-free determination of measured values, potential separation between the measurement position and the electronic analysis system, PA1 no influence of electromagnetic interference field on the signal, PA1 no transfer of electromagnetic interference fields, and on-contact scanning.
However, a disadvantage of these fiber optic sensors is that, as a result of the fact that the sensors must be guided to the measurement position, the optical fibers used as a light source and light guide are susceptible to contamination when used in a coarse environment, which has direct effects on the measurement result. In addition to this, the movement generator has to be constructed in such a manner that it can also serve as an optical modulator, which means that the toothed wheel or the hexagonal nut must be adapted as an optical modulator in accordance with the additional purpose of application, for example by polished surfaces or light-dark markings.
Furthermore, a fiber optic pressure sensor is also described in publication (VDI) (Association of German Engineers) Reports No. 515, 1984, pages 31-37,in particular page 35) wherein an aperture, set towards the pressure chamber, in the housing of the sensor is sealed by a metal membrane. The metal membrane is illuminated on the rear surface by a transmitting optical fiber. A proportion of the light reflected by the rear surface of the membrane is detected by a receiving optical fiber and appropriately analyzed. The more the pressure rises, the greater is the extent to which the membrane bends. This geometric variation causes a modulation of the light signal.
A similar principle is disclosed in the case of a temperature sensor in the Unexamined Published German Patent Application (German Offenlegungsschrift) No. 3,307,966.
An object of the present invention is to provide an improved fiber optic sensor of the relevant type in such a manner that it can be used without susceptibility to contamination, even in a coarse environment and an adaptation of the movement generator is not required.
According to the invention, these objects are achieved by providing an improved fiber optic sensor device having a light transmitter, a light guide, and an optical modulator disposed in a housing. The optical modulator part is moveable relative to the light transmitter and light guide. A permanent magnet cooperates with a modulator part. The magnet responds to movement of a ferromagnetic movement generator and the modulator part correspondingly responds whereby a change in the light signal is analyzed by electronic analysis system connected downstream.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.